1. Field of the Invention
The present invention relates to an electron microscope, and more particularly, to a method for adjusting a micro-bar of an electron microscope.
2. Description of the Prior Art
The line width or line space on the semiconductor wafer is less than one xcexcm and cannot be inspected by using an ordinary optical microscope. Therefore, a scanning electron microscope (SEM) must be used. The scanning electron microscope is ideal for performing a non-destructive inspection on a production line to accurately inspect the line widths and line spaces on the semiconductor wafer and ferret out errors occurring during the production process. As a reference, the SEM displays a micro-bar that provides timely calibration during the semiconductor process. As the line width and line space are narrowed, the accuracy of the micro-bar must be increased in order to ensure accuracy of the SEM.
Please refer to FIG. 1. FIG. 1 is a perspective diagram of a method for producing a calibration standard of the micro-bar of a prior art electron microscope. The calibration standard is produced according to the theory of light-interference. To produce the prior art calibration standard, an optical mask 16 is positioned between a light 12 and a semiconductor wafer 10. Two rifts 18 in parallel with each other are positioned on the optical mask 16. A photo-resist layer is positioned on the surface of the semiconductor wafer 10 and the light 12 is used to provide rays 14 with a fixed wavelength that pass through the two rifts 18 of the optical mask 16 to form a plurality of stripes 19 on the photo-resist layer. After exposure, development, and photo-resist stripping are performed, a column structure is formed in the area of each stripe 19. The width of the surface of the column structure is the line space of the stripe 19 and is used as the calibration standard.
When calibrating the micro-bar of a prior art electron microscope, the electron microscope is used to inspect the column structure on the semiconductor wafer 10. The width of the surface of the column structure is the calibration standard making the accuracy of the micro-bar equal to the line space of the stripe 19. The line space of the stripes 19 can be calculated according to the distance between the semiconductor wafer 10 and optical mask 16, the wavelength of the ray 14, the distance between the two rifts 18 and the line space of the stripes 19. The line space of the stripes 19 is in direct proportion to the distance between the semiconductor wafer 10 and optical mask 16 and the wavelength of the ray 14, and is in inverse proportion to the distance between the two rifts 18.
The smallest line space of the stripes 19 using current technology is about 0.24 xcexcm. In other words, the accuracy of the micro-bar after adjustment is 0.24 xcexcm. In 0.1 xcexcm semiconductor processing, the line width and line space on the semiconductor wafer cannot be accurately measured. Also, the prior art method for adjusting the electron microscope requires a special instrument for providing a specific light 12, an optical mask 16 and the appropriate distance from the semiconductor wafer 10 to optical mask 16. Therefore, the prior art calibration standard cannot be produced by an ordinary semiconductor facility.
It is therefore a primary objective of the present invention to provide a method for adjusting a micro-bar of an electron microscope to solve the above mentioned problems.
Briefly, in a preferred embodiment, the present invention provides a method for adjusting a micro-bar of an electron microscope comprising:
forming a photo-resist layer on a semiconductor wafer;
exposing a predetermined region of the photo-resist layer to a light of a specific wavelength;
performing a resist stripping process to remove the photo-resist layer in the predetermined region wherein the periphery of the predetermined region of the photo-resist layer will form a vertical side wall with a periodic wave shape similar to a sine wave, and the wavelength of the periodic wave shape is determined by the wavelength of the light and the refraction rate of the photo-resist layer; and
adjusting the micro-bar of the electron microscope using the wavelength of the periodic wave shape on the vertical side wall.
It is an advantage of the present invention that the method uses the wavelength of the periodic wave shape on the vertical side wall of the column structure to adjust the micro-bar of the electron microscope so as to improve the accuracy of the micro-bar to 0.07 xcexcmxcx9c0.06 xcexcm. Therefore, the method can be conveniently used in 0.1 xcexcm semiconductor processing to enable the electron microscope to correctly measure the line width and line space on the semiconductor wafer.
These and other objects and the advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.